Blood processing filter

1. A blood processing filter comprising:

a container having two spouts serving as an inlet for a liquid to be processed and an outlet for the processed liquid; and

a filtration medium contained in the container,

the filtration medium comprising a plurality of layers of filter materials, each layer having one surface A and another surface B,

both the surface A and surface B are hydrophilic polymer coating layers, and

the surface A and the surface B having different critical wetting surface tension (CWST) values.

2. A blood processing filter according to claim 1 , wherein a CWST value for surface A in each layer of the filter materials is 72 mN/m or more.

3. A blood processing filter according to claim 1 , wherein a difference in CWST values for surface A and surface B in each layer of the filter materials is 3 mN/m or more.

4. A blood processing filter according to claim 3 , wherein the filtration medium comprises a plurality of filter materials comprising a fibrous medium made of fibers having a fiber diameter of less than 4 μm as a base material,

and wherein a CWST value for a surface of a layer of a filter material among the plurality of filter materials that is located closest to one spout of the container, such surface being on the side with the spout, is greater than a CWST value for a surface of a layer of a filter material among the plurality of filter materials that is located closest to the other spout of the container, such surface being on the side with the other spout.

5. A blood processing filter according to claim 1 , wherein a ratio of a CWST value for surface A to a CWST value for surface B in each layer of the filter materials is 1.03 or more.

6. A blood processing filter according to claim 5 , wherein the filtration medium comprises a plurality of filter materials comprising a fibrous medium made of fibers having a fiber diameter of less than 4 μm as a base material,

and wherein a CWST value for a surface of a layer of a filter material among the plurality of filter materials that is located closest to one spout of the container, such surface being on the side with the spout, is greater than a CWST value for a surface of a layer of a filter material among the plurality of filter materials that is located closest to the other spout of the container, such surface being on the side with the other spout.

7. A blood processing filter according to claim 1 , wherein a CWST value for the one surface A is 72 mN/m or more and 110 mN/m or less, and a CWST value for the other surface B is 60 mN/m or more and 110 mN/m or less.

8. A blood processing filter according to claim 7 , wherein the filtration medium comprises a plurality of filter materials comprising a fibrous medium made of fibers having a fiber diameter of less than 4 μm as a base material,

and wherein a CWST value for a surface of a layer of a filter material among the plurality of filter materials that is located closest to one spout of the container, such surface being on the side with the spout, is greater than a CWST value for a surface of a layer of a filter material among the plurality of filter materials that is located closest to the other spout of the container, such surface being on the side with the other spout.

9. A blood processing filter according to claim 1 , wherein the filtration medium comprises a filter material comprising a fibrous medium made of fibers having a fiber diameter of 4 μm or greater as a base material, and a filter material comprising a fibrous medium made of fibers having a fiber diameter of less than 4 μm as a base material.

10. A blood processing filter according to claim 1 , wherein the filtration medium comprises a plurality of filter materials comprising a fibrous medium made of fibers having a fiber diameter of less than 4 μm as a base material,

and wherein a CWST value for a surface of a layer of a filter material among the plurality of filter materials that is located closest to one spout of the container, such surface being on the side with the spout, is greater than a CWST value for a surface of a layer of a filter material among the plurality of filter materials that is located closest to the other spout of the container, such surface being on the side with the other spout.

11. A blood processing filter according to claim 1 , wherein the filter materials comprise nonwoven fabric.

12. A blood processing filter according to claim 9 , wherein the polymer has a nonionic hydrophilic group and a basic nitrogen-containing functional group, and the amount of basic nitrogen atoms in the polymer coating layer is from 0.2 to 8.0 mass %.

13. A blood processing filter according to claim 9 , wherein the polymer has a functional group comprising a zwitterion.

14. A blood processing filter according to claim 13 , wherein the functional group comprising a zwitterion is a functional group derived from at least one type of compound selected from the group consisting of carbobetaine, sulfobetaine, and phosphobetaine.

15. A blood processing filter according to claim 13 , wherein the polymer comprises a monomer unit ( 1 ) having a nonionic group, a monomer unit (m) having a basic nitrogen-containing functional group, and a monomer unit (n) including a zwitterion.

16. A method for manufacturing a blood processing filter according to claim 1 , the method comprising: preparing a filter base material; and coating both the surface A and surface B of the base material with a hydrophilic polymer using a gravure coating method.